1. Field of the Invention
The present invention relates to an image forming apparatus and more particularly to a paper feeding apparatus for an image forming apparatus capable of detecting both a paper type and paper entrance into a paper transferring path by using a media sensor, and a controlling method thereof.
2. Background of the Related Art
Generally, an image forming apparatus such as laser printer, facsimile, copying machine or multifunction machine performs the printing job by transferring an image corresponding to a data signal input from inside/outside through a photoconductive drum, onto a printing media, i.e., a printing paper provided by a paper feeding system.
For such an image forming apparatus, various types of media, such as ordinary paper, transparent paper, high glossy paper and fabric can be used. Since such a variety of printing media require different printing conditions, such as heating temperature and speed, there is an image forming apparatus having a media sensor for detecting a printing media type so that appropriate printing can be performed automatically according to the printing media type.
A paper feeding apparatus for the image forming apparatus having such a media sensor of a related art is described below with reference to FIG. 1 through FIG. 3.
FIG. 1 is a drawing, schematically illustrating the paper feeding apparatus having a conventional media sensor. As shown in FIG. 1, the paper feeding apparatus includes a pick-up roller 11 for picking up a paper to be printed, a driving roller 12 for transferring the picked-up paper, a feeding roller 13 for providing a paper so that the printing job is performed, a pick-up sensor 21 for detecting whether a paper is picked up, and a media sensor 22 for detecting a paper type.
The pick-up roller 11, being rotated by a pick-up motor (not shown), picks up a paper to be printed and transfers the paper onto a paper transferring path. The paper transferring path is denoted by a bold solid line in FIG. 1. The driving roller 12, being rotated by a line feeding motor (not shown), transfers the paper transferred by the pick-up roller 11 to a predetermined position. The feeding roller 13 is rotated by a line feeding motor (not shown) and transfers the paper to a predetermined position so that the paper can be printed at a printing head (not shown). The pick-up sensor 21 is installed at a predetermined position on the paper transferring path to detect whether a paper is picked up by rotation of the pick-up roller 11 and enters the paper transferring path, and to apply a resultant signal to a controller for controlling the paper feeding apparatus.
FIG. 2 is a circuit diagram illustrating the circuit construction of such a pick-up sensor 21. The pick-up sensor 21 includes a photo interrupter and is configured such that light is blocked by a paper entering the paper transferring path, and the pick-up sensor 21 provides a paper entrance determination signal to a controller 20. When the paper entrance determination signal is provided from the pick-up sensor 21, the controller 20 judges that a paper is picked up and enters the paper transferring path.
At the time that the paper is aligned before being provided to the printing head for printing, the paper is near the media sensor 22 and accordingly, the media sensor 22 is turned on. For a media sensing system for judging a paper type, a combination of light emitting/receiving sensors is used.
FIG. 3 illustrates a driving circuit that drives the media sensor 22. A light receiving unit of the media sensor 22 includes two phototransistors 25a and 25b installed at different angles respectively with respect to the surface of a paper. A light emitting unit includes a resistor 26a connected in series between a power voltage (of 5 V for example) and a ground voltage, and a LED (Light Emitting Diode) 26b. The LED 26b projects light onto a paper passing over the drive roller 12.
Light from the LED 26b is reflected from the paper and incident on the phototransistors 25a and 25b installed at different angles with respect to the paper. Since the phototransistors 25a and 25b are at different angles with respect to the paper, incident light reflected from a paper is in different quantities, and therefore, different outputs are input from the phototransistors 25a and 25b to the controller 20. The controller 20 calculates a ratio of the outputs from the phototransistors 25a and 25b, analyzes the reflective rate of the paper and accordingly determines the paper type. A database having information regarding paper types in relation to ratios of outputs from the phototransistors 25a and 25b is set in advance experimentally.
As described, the conventional paper feeding apparatus requires the pick-up sensor for sensing whether a paper is picked up and enters the paper transferring path as well as the media sensor for sensing a paper type, respectively. Therefore, mechanical construction for installing each sensor on the paper transferring path is complex, and costs for parts are increased due to the use of additional parts.